The automatic pallet changer (APC) is used in the automatic manufacturing system and is mainly composed of two pallets which are interchangeable in position. Each of the two pallets is provided thereon with a workpiece such that the workpiece on one of the pallets is located in the manufacturing and finishing position, and that the workpiece on the other one of the pallets is involved in a pallet changing operation, thereby resulting in the reduction in the waiting time of conventional operations in which the workpieces are loaded on the machine or unloaded from the machine
As shown in FIG. 1, a conventional APC is formed of a pallet lifting mechanism 1 and a revolving mechanism 2. When a pallet 5 is raised by the pallet lifting mechanism 1, the pallet 5 is subsequently changed and rotated by the revolving motion brought about by the revolving mechanism 2. Upon completion of the changing operation, the pallet 5 is lowered and then located by the lifting mechanism 1. The revolving mechanism 2 has a gear 3, which is actuated to move up and down along with the lifting mechanism 1. In order to make sure that the moving range of the gear 3 is so coordinated that the gear 3 meshes well with a rack gear member 4 of the revolving mechanism 2, the gear 3 is thicker and greater in volume. As a result, the gear 3 takes up a relatively large space. In light of the wear brought about by the constant friction between the gear 3 and the rack gear member 4, the gear gap tends to so enlarge that operational precision is seriously undermined. Moreover, the pallet 5 is initially located by means of the gear 3 and the rack gear member 4 and is finally located by the locating portion 6 which is located under the pallet 5. The enlargement of the gear gap can undermine the precision with which the pallet is initially located by the gear body.